1. Field of the Invention
This invention relates to alkoxy functional polydiorganosiloxanes, a method of their preparation, and room temperature vulcanizable silicone elastomers made using the alkoxy functional polydiorganosiloxanes.
2. Background Information
One of the methods of producing silicone sealants is based upon the use of alkoxy endblocked polymers and a titanium catalyst. Such sealants are stable in the absence of moisture, but cure in the presence of moisture to a silicone elastomer. A distinguishing feature of this system over other moisture-curing systems is the absence of acidic or corrosive by-products produced during the curing process.
In storage tubes, many moisture curing sealants often exhibit, over long storage periods, gradual curing due to reaction with moisture. When use of this sealant is attempted, the sealant cannot be expelled from the storage tube because it is too viscous or it has completely cured. In contrast to this, the alkoxy-titanate room temperature vulcanizable (RTV) silicone elastomer compositions gradually loose the ability to cure with time of storage. This is particularly undesirable because the sealant can be expelled from the tube into the desired location for sealing without the user being aware that there is anything wrong. It is only after the sealant fails to cure that a problem becomes apparent, and by then it is too late as the sealant is already in place. It is then necessary to physically remove all of the old non-curing sealant and replace it with new. This is a very time consuming and expensive process. Because of this type of failure mode, it became imperative that a method of producing a non-acid, non-corrosive RTV silicone sealant be developed that would overcome this non-curing failure upon storage.
There are many patents directed to producing silicone sealants based upon the use of alkoxy functional polymers, alkoxy functional crosslinkers, and titanate catalysts. Representative of these is U.S. Pat. No. 3,334,067, issued Aug. 1, 1967, to Weyenberg. Weyenberg discloses a method of making one component room temperature curing siloxane rubber. His compositions are stable in the absence of moisture, but cure upon exposure to moisture. The method comprises mixing in the absence of moisture a hydroxy endblocked siloxane polymer, a silane of the formula R*Si(OR**).sub.3 and a beta-dicarbonyl titanium compound. R* is a monovalent hydrocarbon radical, a monovalent halohydrocarbon radical, or a monovalent cyanoalkyl radical all having from 1 to 18 carbon atoms per radical. R** is an aliphatic hydrocarbon radical or a haloaliphatic hydrocarbon radical of less than 5 carbon atoms per radical.
In U.S. Pat. No. 3,383,355, issued May 14, 1968, Cooper discloses polymers having alkoxy groups bonded to terminal silicon atoms by reacting a hydroxylated organosiloxane polymer with an alkoxy silane in the presence of a suitable catalyst. He discloses that such functional diorganopolysiloxanes having from two to three alkoxy radicals attached to each terminal silicon atom are curable to a rubbery material in the presence of moisture and a suitable hydrolysis and condensation catalyst.
Smith et al., in U.S. Pat. No. 3,856,839, issued Dec. 24, 1974, disclose alkanedioxy titanium chelates which catalyze the cure of a composition which also contains methyltrimethoxysilane and a silanol chain-stopped polydiorganosiloxane fluid. The alkanedioxy titanium chelates are stated to be desirable because they do not cause thickening during the manufacture of the composition as do the previously known titanium compounds.
An improved version of the Smith et al compositions is disclosed by Getson et al. in U.S. Pat. No. 4,111,890, issued Sep. 5, 1978, in which the hydrocarbonoxy groups linked to the organopolysiloxane, organosilicon compound and the titanium ester groups are the same. They disclose that previous compositions have a short shelf-life even when kept under substantially anhydrous conditions, and that the longer these compositions are stored, the property profile deteriorates.
Beers et al in U.S. Pat. No. 4,438,039, issued Mar. 20, 1984, disclose that the shelf life of some commercial compositions was determined by an appearance problem, manifesting itself in the formation of various sizes of crystals ranging from fine sand-like to pellet-like particles. This patent discloses a particular titanium catalyst which does not form nodules upon storage.
The above prior art does not disclose solutions for the problem of failure to cure after prolonged storage. After an extensive investigation into the possible causes of such a storage failure, the solution to the problem was discovered. Once the solution to the problem is known, other background information becomes of interest.
Brown et al in U.S. Pat. No. 3,122,522, issued Feb. 25, 1964, disclose a siloxane composition, each molecule of which consists essentially of at least two units of the formula EQU [R**(OCH.sub.2 CH.sub.2).sub.g O].sub.e (R*.sub.f)SiM(R*.sub.2)SiO.sub.0.5
and units of the formula EQU R*.sub.h SiO.sub.(4-h)/2
where each e has a value ranging from 2 to 3, each f has a value ranging from 0 to 1, the sum of e and f in any unit is no greater than 3, each g has a value ranging from 1 to 2, each h has a value ranging from 0 to 2, R* and R** are selected from monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals, M is a divalent hydrocarbon radical of from 2 to 18 inclusive carbon atoms, and M is free of aliphatic unsaturation. Each molecule of the silicone composition has an average of from 1.3 to 2 R* groups per silicon atom and there are at least 7 units of R*.sub.h SiO.sub.(4-h)/2 per molecule.
U.S. Pat. No. 3,175,993, issued Mar. 30, 1965 to Weyenberg discloses a composition consisting essentially of the average formula ##STR3## in which each R* is free of aliphatic unsaturation, M is a divalent hydrocarbon radical free of aliphatic unsaturation, k has a value of from 0 to 2 inclusive, j has a value of at least 3 and e has an average value from 2 to 3 inclusive.
Both Brown et al and Weyenberg teach preparation of the siloxane by reacting siloxanes containing --SiH groups with the appropriate silane containing an olefinic unsaturated aliphatic or cycloaliphatic group in the presence of a platinum catalyst through the reaction of the --SiH and aliphatic C.dbd.C group. This reaction produces the divalent M radical. Alternatively, the C.dbd.C group can be on the siloxane and the --SiH can be on the silane.
Lucas in U.S. Pat. No. 4,731,411, issued Mar. 15, 1988, discloses a process for producing alkoxy-terminated polysiloxanes useful to produce room temperature vulcanizing silicone rubber compositions. The process anhydrously reacts a silanol or vinyl siloxane with a poly-alkoxy crosslinking agent which is an alkoxy silane in the presence of a platinum catalyst. This alkoxy-terminated polysiloxane can also be mixed with treated filler and condensation catalyst. This application teaches that an alkoxy-terminated polysiloxane having no silethylene linkage at the polymer terminal silicon is equivalent to a polydiorganosiloxane that does contain a trialkoxysilethylene terminal group.
Totten et al in U.S. Pat. No. 4,579,964, issued Apr. 1, 1986, disclose an alkoxysilyl functional silicone including at least one functional group of the formula ##STR4## where t is an integer of from 2 to about 20, which is useful for imparting lubricity and softness to a variety of textile fabrics.
Klosowski et al in U.S. Pat. No. 4,888,404, issued Dec. 19, 1989, describe making silicone sealants which have improve shelf life. These silicone sealants are based on polymers of the general formula R2 ? ##STR5## where R* is methyl, ethyl, propyl, phenyl, or trifluoropropyl, R** is methyl, ethyl, propy, or butyl, e is 0 or 1, f is 0 or 1, g is from 1 to 6 and s is such that the viscosity is from 0.5 to 3000 Pa.s at 25.degree. C. These polymers are called alkoxysilethylene ended polydiorganosiloxanes. RTV silicone sealants are made by combining these polymers with alkoxysilane crosslinkers, titanium catalysts, and fillers. Klosowski et al improve the shelf stability of RTV silicone sealants through the use of their polymers, also improve the cure rate while maintaining or improving the storage stability of the RTV sealants.